1. Field of the Invention
The present invention relates to a powdery detergent composition comprising a nonionic surfactant as a main base and a process for producing the same, and more particularly to a powdery detergent composition which does not cause any deterioration with respect to its solubility during storage, and a process for producing the same.
2. Description of the Related Art
A nonionic surfactant has various features such as good hard water resistance and, at the same time, prominent detergency and capability of dispersing soil, and further very excellent biodegradability, so that it is deemed to be an important surfactant for washing.
However, since many nonionic surfactants used for washing purposes are usually liquid at ordinary temperatures, they have the problem that when they are incorporated in a liquid state in a powdery detergent composition in a large amount, they gradually bleed out with the lapse of time and penetrate into the inside of the paper container which holds the detergent composition, which remarkably deteriorates the fluidity of the powdery detergent composition or brings about caking to render the detergent composition massive, which remarkably deteriorates the commercial value of the detergent composition. These problems have led to various studies.
U.S. Pat. No. 4136051 (published on Jan. 23, 1979, Assignee: Henkel KGaA) discloses a detergent composition having an improved fluidity and comprising a premixture composed of a crystalline or amorphous aluminosilicate having an ion exchange capacity of 50 mg CaO/g (89 mg CaCO.sub.3 /g) or more (4% or less of a highly dispersive silica may be used as an oil absorbent carrier), a nonionic surfactant and optionally an inorganic peroxide capable of forming hydrogen peroxide in water and, incorporated into the premixture, a spray-dried detergent composition. Great Britain Patent No. 1474856 discloses a detergent composition having an improved fluidity and comprising a mixture of a synthetic amorphous silica derivative (including an aluminosilicate) having an oil absorbability of 50 to 200 cm.sup.3 /100 g with a nonionic surfactant and a phosphoric chelating agent. Further, Japanese Patent Laid-Open No. 89300/1986 discloses a process for producing a granulated detergent composition having excellent powder properties and produced by mixing a water-soluble powder with a silica powder, spraying the mixture with a nonionic surfactant and adding a zeolite or calcium carbonate powder thereto. Furthermore, U.S. Pat. Nos. 5,080,820 and 5,024,778 disclose a nonionic powdery detergent composition containing spray-dried beads comprising an aluminosilicate and bentonite and having a water-soluble silicate content of 5% by weight or less.
As described above, it is known that the incorporation of a siliceous substance or a clayey substance, such as bentonire, into a detergent composition containing a nonionic surfactant contributes to an improvement in the powder properties of the detergent composition, such as fluidity.
In fact, the use of the siliceous substance or the clayey substance as an oil-absorbent carrier serves to prevent the nonionic surfactant from bleeding. However, there is a tendency that the solubility of the detergent composition lowers during storage for a long period of time under high-humidity conditions and, in addition, when the detergent composition contains a water-soluble alkali metal silicate such as water glass, the solubility of the detergent composition remarkably lowers.
This requires a further improvement in the solubility after the lapse of time of a powdery detergent composition containing a nonionic surfactant.